Practically all metal articles in commerce today--ranging from simple nuts and bolts to automobile bodies and beyond--have been subject to some type of pretreatment to modify and improve the physical or chemical properties of the metal surfaces. Phosphating is the most widely used metal pretreatment processes. Zinc phosphating is the most widely used of the phosphating pretreatment processes, with iron phosphating and manganese phosphating being used less often.
The treatment of iron, steel, and other metals with zinc phosphate compounds has been used for decades, if not longer, to improve corrosion resistance, paint bonding, lubrication during metal forming operation, and electrical characteristics of the treated metal surfaces. Iron and manganese phosphate compounds have also been used for the treatment of such metal surfaces. These phosphate solutions chemically react with a metal surface to covert that surface into a crystalline phosphate coating. The phosphate coating imparts the desirable properties to the metal surface. Due to the chemical reactions involved, undesirable by-products (i.e., phosphate sludge) are formed in, and settle out of, the baths. Although the composition of the phosphate sludge will vary depending on the composition of the phosphating baths, the metals treated, and the treatment conditions, generally the phosphate sludge will contain significant portions of zinc primary phosphate, zinc tertiary phosphate, ferrous phosphate, ferric phosphate, and/or manganese phosphate. Such phosphate sludges are generally considered as hazardous waste materials under U.S. Environmental Protection Agency (EPA) regulations at 40 C.F.R. Part 261 and are, therefore, subject to strict regulation as to disposal. These waste materials must, therefore, either be subjected to approved waste treatment on site or trucked to an approved waste treatment facility. Generally, disposal of the phosphate sludge involves collecting the material, dewatering the sludge to reduce transportation costs, and transporting the dewatered sludge to an approved landfill. Considerable costs and environmental risks are involved in such treatment and disposal.
Recently, in U.S. Pat. No. 4,986,977, a method for treating the sludge formed in a zinc phosphate conversion bath was described whereby various compounds are recovered from the sludge material. In a preferred embodiment (illustrated in FIG. 2 of that patent), the sludge was first treated with an aqueous base at a pH of at least 10 whereby solid iron hydroxide was recovered from a first aqueous phase. This first aqueous phase was then treated with an alkaline earth meal base at a pH greater than 10 whereby solid metal phosphate was recovered from a second aqueous solution. This second aqueous phase was then treated with acid at a pH of 7 to 10 whereby solid zinc hydroxide was recovered from a third aqueous solution. This third aqueous solution is reported to contain "soluble alkali metal salts essentially free of phosphate ions." Although this process is an improvement over direct disposal of the phosphate sludge, it does not eliminate the waste disposal problem. In addition to the disposal of the third aqueous solution, the solid products collected may also contain at least small concentrations of toxic contaminants which may render the utilization or disposal of the solid products more difficult.
It would be desirable to provide a method by which phosphate sludge could be recycled and converted to a useful product in its entirety. It would be desirable to provide phosphate conversion bath processes where disposal of the phosphate sludge is not required or is at least significantly reduced. It would also be desirable to provide new lubricant additives and lubricant formulations for metal forming, metal working, and other lubrication operations. It would also be desirable to provide a new and effective Extreme Pressure Additive for such lubrication operations and system. This present invention achieves these objectives as fully described in this specification.